Furthermore, South Korea's Yonhap news agency reports that, following a successful nuclear test, North Korea carried out a total of three test launches of short-range ground-to-air missiles, RIA Novosti news agency says.

Seismologists in Russia’s Far East confirmed the breaking news.

“Judging by the data we received from the Far East it looks rather unusual. We’ve registered it as a seismological event, but the data is rather unusual. It may be an earthquake but it looks like an explosion,” said seismologist Yury Levin.

There have been conflicting reports concerning the magnitude of the earthquake, with the US geophysicists saying that the earthquake registered about 4.5 points at Richter scale, while Russian ones are claiming it was around 5.1 points.

According to Russian Defense Ministry spokesman, Colonel Aleksandr Drobyshevsky, an underground nuclear explosion equivalent to 10-20 kilotons was registered at 04:54 Moscow time on May 25.

Also, a high-ranking official from the Russian Defence Ministry told Itar-Tass that the test “was made at the same location in the northeast of North Korea where the first nuclear underground test was conducted in 2006."

“In case of persistence on its nuclear programme the leadership of North Korea could face a strict sanctions regime, and thus put its people on the brink of a humanitarian catastrophe. <…> So I am sure that at today's meeting of the UN Security Council, the condemnation of North Korea's actions will be unanimous. Pyongyang must understand that they won’t be able to keep toying with us.”

Mikhail Margelov, Chairman of the Federation Council on International Affairs

Back then the test was equivalent to 5-15 kilotons, then Russian Defense Minister Sergey Ivanov said.

In comparison, the uranium bomb dropped on Hiroshima in 1945 was equivalent to 15 kilotons, and the Nagasaki one – to 21 kilotons.

The news didn’t come out of the blue for leading policymakers, according to Kyodo news agency. It cites a source in the US administration as saying Pyongyang notified them of the upcoming test some hours before the event, although no detail on the characteristics of the test or its timing was revealed. Washington passed the news over to Seoul, Tokyo, Moscow, Beijing and others. The report, however, contradicts an official statement by Japan, according to Itar-Tass agency. Unofficial reports from Russia say otherwise too.

International reaction

The UN Security Council has unanimously condemned North Korea’s nuclear test as a clear violation of its resolutions. The body held a closed emergency meeting at Japan's request on Monday evening.

In a statement released after the consultations, the council said it would begin work immediately on a new legally binding resolution concerning the North Korean nuclear issue.
“Today we made no effort to come up with a definitive response from the Security Council because it will take some time. But we felt it was necessary to give an immediate response,” said Vitaly Churkin, Russia’s Ambassador to the UN, after the meeting.

Earlier on Monday the reaction from the west was strongly critical.

President Barack Obama has called the North Korean nuclear test “a challenge to the world community.”

British Prime Minister Gordon Brown condemned the test as "erroneous, misguided and a danger to the world."

“We absolutely need to condemn those tests. I find it right that the UN Security Council is meeting. We should do our best to make sure that these talks start again and North Korean isolation will come to an end,” said Germany’s Chancellor Angela Merkel.

“I hope the Security Council will take the necessary responsive measures,” said UN Secretary General Ban Ki-Moon.

Similar sentiments came from other states, particularly Asian ones.

“The testing is a flagrant violation of the existing UN Security Council resolutions, and the government of Japan strongly protests against North Korea for this nuclear testing,” commented Kazuo Kodama, Press Secretary, Japanese Ministry of Foreign Affairs.

South Korea has condemned the new nuclear test conducted by North Korea, saying it is “a serious threat and a challenge” to the whole world community. The South Korean President’s spokesman, Lee Dong-Kwan, said that Seoul is planning to urge the UN Security Council to take active counter-measures.

South Korea and Japan have agreed on pushing for North Korea to be punished by the UN, Itar-Tass also reports.

South Korean visitors look at the North Korean side at an observation tower in Paju in the South, about 45 kms (28 miles) north of Seoul near the border that separates the countries (AFP Photo / Kim Mi-Ok)

China was resolutely opposed to North Korea’s nuclear test, the country’s Foreign Ministry said in a statement according to Xinhua news agency.

The statement voiced a strong demand that North Korea “live up to its commitment to non-nuclearization on the Korean Peninsula, and stop any activity that might worsen the situation and return to the track of the six-party talks.”

The US said that though North Korea’s actions haven’t come as a surprise after what it had been saying and doing lately, they are a matter of grave concern to all nations.

Meanwhile, a high-ranking official from the South Korean President’s administration has claimed that North Korea warned the US authorities about the nuclear test in advance, Itar-Tass news agency reports.

The source also said that South Korean special services had been monitoring the test preparations: “That test was not a surprise for us as we expected it and kept an eye on the site where it was conducted.”

“A serious threat of nuclear conflict is coming into being at our borders. Proliferation of these weapons on the planet is very dangerous. Therefore, I believe Russia should take an active stance in the UN Security Council during the discussions on the matter and, if necessary, insist on application of economic sanctions against North Korea.”

"These irresponsible acts by North Korea warrant a firm response by the international community. The European Union will be in contact with its partners to discuss appropriate measures," Solana said.

Russia denounces North Korea's nuclear test

Kremlin has labelled North Korean underground nuclear test a direct violation of UN security council resolution.

Still, Russia's Foreign Ministry has made a statement urging Pyongyang to display “a responsible attitude for the sake of stability in the region” and saying that “only six-party talks may resolve the North Korean nuclear problem.”

"The latest steps of North Korea have escalated tensions in Northeast Asia and endangered regional security and stability. Recognizing the lawful concerns of North Korea, we do not see any real alternative in the provision of its security other than political and diplomatic efforts and the formation of relevant regional institutions with the participation of all interested sides," the Ministry said.

Russia is concerned with what’s happening on the peninsula because North Korea is a neighboring country, although the border between them is only about 18 kilometres long.

Even so, should any nuclear incident occur on the peninsula, Russia would be one of the first countries affected.

Russia’s Foreign Minister Sergey Lavrov, who is now on visit to Lebanon, has expressed his concerns over the issue.

“Japan suggested convening the UN Security Council today at 16:00 NYC time, and the delegations of the countries that have seismic monitoring stations should have information by that time which will help us understand what exactly happened,” Lavrov said.

North Korea's nuclear ambitions

It is hard to say at the moment what North Korea is trying to gain from this nuclear test, but one of the things that nuclear experts are talking about is the fact that Pyongyang is trying to set itself as a major player in the world arena, and attract attention to what is happening on the peninsula.

“A couple of years ago, when North Korea performed its first nuclear test, its authorities agreed to hold talks under pressure from the international community. Maybe now the UN needs to show a more rugged approach to the issue, including possible implementation of sanctions against North Korea.”

Igor Barinov, First Deputy Chairman of Russia’s State Duma Committee on Defense

A source from the Russian Foreign Ministry said that "the most important thing at the moment is not to go off into hysterics and overreact, as unfortunately happened after North Korea's rocket launch."

“The situation is difficult, as it concerns the implementation of UN Security Council's resolutions, guarantees of stability, of non-proliferation and on the whole, prospects for solving the nuclear problem on the Korean peninsula," the source added.

Last month, Pyongyang pulled out of six-nation talks including Russia and the United States, which were convened to deal with the communist country's nuclear programme.

It also warned that it would revive the programme and carry out new tests.

The chances to get N.Korea back to negotiation table

Analysts say that urging Pyongyang to return to negotiations will be one difficult task. Those who have been to North Korea say that learning what’s on the mind of the people there is even harder, as North Koreans are a very secretive people. Experts are now trying to determine what exactly Pyongyang is trying to achieve by deliberately infuriating the world community.

“North Korea now wants to show it is a nuclear power and wants to set its own terms during negotiations,” supposes Georgy Toloraya, Director of Korean Programmes.

Russia has vast experience in underground nuclear weapon tests. In Soviet times, hundreds of such experiments were held with no consequences. Environmentalists in the country’s Far East do not fear any ecological disasters following this test in North Korea. But clearly, Russia has a reason to be worried, being North Korea’s neighbour.

The borderline between Russia and North Korea is only 18 kilometers long, and Russia would be one of the first countries to be affected should any nuclear incident happen on the peninsula. So Moscow will be pressing for the quickest possible solution to this issue at the negotiating table.

Konstantin Kosachev, the Head of the Foreign Affairs Committee of the Russian State Duma, says these tests show that North Korea isn't scared of sanctions.

“Further sanctions could be counterproductive because North Korea has already demonstrated that it will not accept any sanctions. This country is ready to exist under any hard sanctions implemented by the international community. So, sanctions do not bring a solution: it lies at the negotiating table. We need to motivate North Korea to come back to this table.”

North Korea's latest nuclear test shows that its nuclear programme has evidently been making progress, Colonel General Viktor Yesin, an authoritative Russian expert and former chief of the Russian Strategic Rocket Forces' General Staff, told Interfax-AVN on Monday.

"North Korea had produced a total of 38.5 kilograms of weapon-grade plutonium by 2009. Of this amount, 2.1 kilograms were used during the nuclear test in October 2006. It is impossible to say now how much plutonium was used during the May 25 test. Given the announced yield of the nuclear explosion, it could be equivalent to four-five kilograms. This is my tentative estimate," Yesin said.

According to Yesin, the remaining plutonium is most likely being used to make nuclear ammunition.

"Some experts suggest that North Korea could have up to six samples of nuclear ammunition with simplified plutonium implosive nuclear charges," he said.

Yesin believes that Pyongyang will be able to allocate another eight kilograms of weapons-grade plutonium from its irradiated nuclear fuel stockpiles in the near future and it will allow North Korea "to produce two more samples of nuclear ammunition."

As for the consequences of the test for North Korea, Yesin said that the UN Security Council will most likely adopt yet another resolution condemning Pyongyang, "though it would be naïve to expect North Korea to obey to it. Out of all members of six-party talks which have been held since 2003, only Beijing possesses real leverage to influence Pyongyang as North Korea’s economic situation is fully dependent on supplies from China."